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m  tije  Citj>  of  J9eto  gorfc 

COLLEGE  OF  PHYSICIANS 
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AN 

INAUGURAL  DISSERTATION 

ON 

RESPIRATION. 

SUBMITTED  TO  THE  PUBLIC  EXAMINATION  OF  THE 

FACULTY  OF  PHYSIC 

UNDER  THE  AUTHORITY  OF  THE  TRUSTEES  OF  COLUMBIA  COLLEGE, 
IN  THE  STATE  OF  NEW-YORK, 

."he  Right  Rev.  BENJAMIN  MOORE,  D.D.  President; 

FOR  THE  DEGREE  OF 

DOCTOR  OF  PHYSIC, 

On  the  12th  Day  of  November,  1805. 


BY  THOMAS  COCK, 

CITIZEN  OF    THE   STATE   OF   NEW-YORK, 


Hear,  O  ye  sons  of  time !  the  powers  of  life 
Arrest  the  elements,  and  stay  their  strife ; 
From  wandering  atoms,  ethers,  airs,  and  gas, 
By  combination  form  the  organic  mass ! 
And, — as  they  seize,  digest,  secrete, — dispense 
The  bliss  of  being  to  the  vital  ens. 

Darwin, 


NEW-YORK; 


Ptfnwd  by  T.  &  J.  SWORDS,  Printers  to  the  Faculty  of  phy»ic 
of  Columbia  College,  No.  160  Pearl-ttreet. 

1805. 


71/ 
/mr 


TO 

VALENTINE  SEAMAN,  M.  D. 

Permit  me  to  offer  you,  as  a  mark  of  esteem  and  respect, 

the  first  fruits  of  that  medical  education  which  has 

been  conducted  under  your  patronage. 

The  AUTHOR. 


to 
WILLIAM  HAMERSLEY,  M.D. 

Professor  of  the  Theory  and  Practice  of  Physic  in  Columbia  College, 

THIS  DISSERTATION 

Is  respectfully  inscribed 

By  his  obliged  humble  servant 

The  AUTHOR, 


INTRODUCTION. 


WHEN  we  take  a  retrospective  view  of  the 
advancements  that  have  been  made  in  physiolo- 
gical inquiries,  we  are  fully  impressed  with  the 
advantages  that  have  resulted  from  a  correct 
chemical  examination  of  the  materials  operating 
upon  the  animal  body,  together  with  a  more  ac- 
curate investigation  of  its  productions.  Among 
the  agents  acting  upon  the  body,  and  entering 
into  it  as  an  useful  part,  the  aix  of  the  atmosphere 
demands  the  greatest  attention ;  and  in  this  che- 
mical inquiry  has  been  productive  of  extensive 
importance. 

It  is  certain  that  the  most  important  advant- 
ages do  result  from  a  close  attention  to  the  dif- 
ferent functions  of  the  animal  body  in  a  state 
of  disease;  therefore,  in  proportion  as  our 
knowledge  of  these  functions  is  more  or  less 
correct  in  a  state  of  health,  so  may  the  diseased 
changes  of  the  body  be  inferred,  and  their  re* 


(  i  ) 

moval  understood.  With  an  impression  of  this 
nature  I  have  been  led  to  the  investigation  of 
Respiration  as  the  subject  of  an  Inaugural  Essay. 

From  the  late  experiments  of  some  ingenious 
chemists  who  have  directed  their  attention  par- 
ticularly to  this  subject,  many  important  facts 
have  been  discovered.  Among  these  experi- 
menters may  be  reckoned  Dr.  Beddoes  and 
Mr.  Davy;  the  latter  of  whom  has  exposed, 
with  great  clearness,  the  fallacy  of  preceding 
opinions,  and  has  given  more  extensive  expe- 
riments upon  the  nature  of  different  airs,  with 
their  effects  upon  the  body  when  respired. 
These  experiments  have  not  only  been  made 
upon  himself,  but  upon  others  with  the  greatest 
attention. 

However  clear  and  decisive  the  experiments 
of  Dr.  Goodwin  upon  respiration  may  have 
been  considered,  Mr.  Davy  has  pointed  out  their 
errors  and  imperfections,  and  has  deduced  from 
his  own  discoveries  a  more  correct  explanation 
of  the  phenomena  of  this  function. 

In  the  plan  of  this  dissertation  each  particu- 
lar division  is  briefly  considered.  In  the  first 
place  a  short  sketch  is  given  of  the  parts  con- 
cerned in  the  performance  of  respiration. 


(  7  ) 

2d.  The  importance  of  air  in  the  support  of 
life,  and  its  chemical  properties  are  considered. 

3d.  The  influence  of  different  airs  upon 
blood  out  of  the  body,  and  the  changes  that 
are  effected  upon  this  in  its  passage  through  the 
lungs  of  animals  during  life. 

4th.  The  application  of  these  different  phe- 
nomena to  the  explanation  of  animal  heat. 

In  the  explanation  of  many  subjects  in  phy- 
siology great  error  has  arisen  from  too  general 
conclusions  by  analogical  reasoning,  and  this 
by  facts  drawn  from  the  operation  of  matter 
upon  inanimate  substances.  Hence  the  reason- 
ing has  been  fallacious,  as  the  laws  of  inanimate 
matter  are  far  different  in  their  operations,  sub- 
ject to  great  variety  from  the  actions  of  the  ma- 
chine itself,  and  changed  by  the  influence  of 
mind  upon  matter,  which  is  primarily  operated 
on  by  a  variety  of  external  as  well  as  internal 
causes.  How  far  these  objections  are  applica- 
ble to  the  present  opinions  on  the  subject  of 
respiration,  time  will  alone  determine,  as  error 
shall  give  way  to  truth,  and  the  absurdity  of 
hypothesis  be  corrected  by  the  power  of  just 
experiments  and  correct  reasoning* 


AN 

INAUGURAL  DISSERTATION 

ON 

RESPIRATION. 

Jt5  Y  Respiration  is  understood  the  taking  in  and 
expelling  air  from  the  lungs.  The  importance  of 
this  function  has  rendered  it  synonimous  with  life. 
We  are  all  sensible  of  the  great  inconvenience  of 
its  being  suspended  only  for  a  short  time,  or  of 
any  imperfection  in  its  performance,  as  takes 
place  in  many  diseases  of  the  chest;  such  as 
asthma,  hydrothorax,  &c.  in  which  a  free  action 
of  the  parts  concerned  cannot  take  place. 

Respiration  is  a  function  of  a  mixed  kind,  that 
is,  both  voluntary  and  involuntary.  We  can 
increase  its  frequency,  and  can  take  in  a  larger 
quantity  of  air  at  will;  but  in  this  case  the  ope- 
ration becomes  fatiguing,  the  same  as  when  any 
motion  is  performed  by  voluntary  muscles  in 
other  parts  of  the  body.*  As  an  involuntary  ac- 
tion, it  is  rendered  far  more  important  to  us,  as 
our  existence  is  so  immediately  connected  with 
its  regular  performance  and  continuance;  and 
whenever  we  make  it  a  voluntary  action,  its  fre- 
quency or  force  is  always  increased. 

The  principal  parts  concerned  in  respiration 
are,  the  trachea,  lungs,  and  diaphragm,  to  which 

*  In.  the  singular  instance  of  Mr.  John  Hunter,  his  respiration  was  a 
complete  voluntary  action  for  some  time;  he  found  it  unnecessary  to 
respire  except  when  he  would  speak. 

B 


(    io    } 

may  be  added,  the  intercostal  and  abdominal  mus- 
cles ;  and  when  it  becomes  forced  or  laboured  from 
any  cause,  other  muscles  are  called  into  action. 

The  trachea  is  a  cartilaginous  tube,  extending 
from  the  larynx  to  the  bronchia,  which  are  its 
divisions,  and  whose  more  extreme  ramifications 
terminate  in  the  air  cells  of  the  lungs.  This  tube 
is  lined  throughout  its  whole  extent  with  a  deli- 
cate membrane  of  extreme  sensibility  to  all  mat- 
ters excepting  air,  and  highly  susceptible  of  in- 
flammation. The  lungs  are  organs  of  consider- 
able size  that  completely  fill  up  the  two  larger 
cavities  of  the  thorax;  they  possess  little  specific 
gravity  in  animals  that  have  breathed,  being 
made  up  of  cells  extremely  numerous  and  minute, 
upon  which  the  branches  of  the  pulmonary  ar- 
tery spread  out :  they  always  contain  air  in 
greater  or  less  quantity,  according  as  they  are 
more  or  less  distended  or  collapsed.  The  lungs 
(contrary  to  the  ancient  opinion)  are  considered 
as  passive  in  the  function  of  respiration;  they 
only  fill  up  the  increased  cavity  of  the  thorax, 
which  is  produced  by  the  actions  of  the  inter- 
costal muscles  elevating  the  ribs;  while  the  dia- 
phragm encroaches  upon  the  abdomen,  which 
it  effects  by  bringing  itself  nearer  to  a  plane; 
and  the  lungs  are  enabled  to  fill  up  what  would 
otherwise  be  a  vacuum  by  air  rushing  into  them 
through  the  trachea.  These  actions  constitute 
inspiration.  The  air  is  again  expelled  from  the 
lungs  by  the  actions  of  the  abdominal  muscles 
which  are  attached  to  the  ribs,  and  are  ex- 
cited into  action  by  their  elevation  and  by  the 


(  11  ) 

protrusion  of  the  abdominal  viscera  produced 
by  the  descent  of  the  diaphragm.     The  expul- 
sion of  the  air  is    also  assisted    by  the    elasti- 
city of  the  cartilages  connected  with  the  ribs; 
by  which  power,  after  the  intercostal  muscles 
cease  to  act,  they  restore  themselves   to  their 
former  situation,  which  diminishes  the  cavity  of 
the  chest  and  empty  the  lungs.    Although  these 
combined  actions  produce  respiration,  yet  it  may 
be  performed  with  a  less  number,  under  certain 
circumstances,  as  where  the  ribs  are  fractured,  or 
in  inflammations  of  the  pleura,  where  motion  is 
rendered  painful:  respiration  takes  place  princi- 
pally by  the  actions  of  the  diaphragm,  in  which  it 
is  an  essential  part.     The  use  of  thus  taking  in 
and  discharging  air  from  the  lungs  was  little  un- 
derstood until  the  time  of  Dr.  Priestley,  although 
many  hints  had  been  thrown  out  by  his  predeces- 
sors of  its  probable  effects.     It  was  with  this,  as 
with  many  other  important  discoveries,  that  when 
its  nature  was  understood,  the  discovery  itself 
explained  the  mysterious  opinions  found  in  the 
writings  of  former  ages,  which  before  were  en- 
tirely inexplicable.    Something  of  this  is  apparent 
in   the  observations  of  Dr.  Beddoes  upon  the 
writings  of  Mayow,  where  he  says,  "  he  not 
only  understood  the  composition  of  the  atmos- 
phere, but  was  also  aware  of  the  increased  weight 
of  metallic  bodies,   and  that  certain  bases  are 
rendered  acid  by  combination  with  vital  air.  He 
also  asserted,  that  the  air  was  diminished  in  res- 
piration, and  that  a  certain  portion  was  conveyed 
to  the  blood.     If  this  be  an  accurate  analysis  of 


(      12     ) 

his  writings,    he    appears   to   have   understood 
almost   the  whole  doctrine  of  respiration  and 
combustion  as  determined  by  modern  chemists. 
The  mysterious  manner  in  which  the  opinions  of 
Mayow  are  expressed,  has  given  rise  to  a  differ- 
ence of  opinion  as  respects  the  merit  which  he 
deserves  as  a  discoverer  of  the  nature  of  the  at- 
mosphere.   The  celebrated  experiments  of  Hook 
(who  was  the  predecessor  of  Mayow)  before  the 
Royal  Society,  appear  to  contain  some  knowledge 
of  the  uses  of  air  in  respiration.     He  laid  open 
the  thorax  of  a  dog,  and  kept  the  animal  alive  for 
some  time  by  blowing  air  into  his  lungs.     These 
experiments  and  facts  could  not  have  come  within 
the  knowledge  of  Dr.  Hunter,  or  he  considered 
them  as  not  having  in  any  degree  developed  the 
nature  of  this  function,  as  we  should  infer  from 
his  introductory  lecture  published  in  1784,  where 
he  says,  "  respiration  we  cannot  explain,  we  only 
know  that  it  is  in  fact  essential  and  necessary  to 
life.     Notwithstanding  this,  when  we  see  all  the 
other  parts  of  the  body  and  their  functions  so 
well  accounted  for,  we  need  not  doubt  that  res-^ 
piration  is  so  likewise.     And  if  ever  we  should 
be  happy  enough  to  find  out  clearly  the  object  of 
this  function,  we  shall  doubtless  as  clearly  see  that 
this  organ  is  as  wisely  adapted  for  an  important 
office,  as  we  now  see  the  purpose  and  importance 
of  the  heart  and  vascular  system;  which  till  the 
circulation  of  the  blood  was  discovered  was  to- 
tally concealed  from  us."     This  has  since  been 
realized  by  the  discoveries  of  Priestley,  Scheele, 
d  Lavoisier^  in  modern  chemistry,  which  have 


{      13     ) 

thrown  great  light  not  only  upon  this,  but  upon 
many  other  functions  of  the  human  body.  fc  The 
establishment  of  this  truth  alone  is  almost  suffi- 
cient to  subvert  the  old  and  to  erect  a  new„system 
of  physiology.  And  if  no  other  benefit  than  this 
had  arisen  from  all  the  brilliant  discoveries  which 
chemistry  offers  to  the  world,  it  would  have  suf- 
ficed to  rescue  that  science  from  neglect,  and  to 
assign  it  an  elevated  rank  among  the  objects  of 
human  knowledge. "  Perhaps  one  of  the  most 
mysterious  operations  of  the  human  body  yet  re- 
mains to  be  explained  by  it,  namely,  secretion. 

The  importance  of  respiration  to  animal  life 
consists  in  a  frequent  change  of  air.  When  ani- 
mals are  deprived  of  this,  they  soon  cease  to  exist, 
as  when  confined  under  the  receiver  of  an  air- 
pump,  where  life  is  terminated  by  convulsions 
as  the  air  becomes  vitiated.  Life  becomes  pain* 
ful  and  imperfect  where  the  same  air  is  breathed 
by  a  number  of  persons,  as  in  large  assemblies; 
or  produces  great  destruction,  as  was  particularly 
exemplified  in  the  distressing  instance  of  Mr. 
Holwell  and  his  companions  in  the  black  hole 
at  Calcutta;  where,  in  consequence  of  a  consi- 
derable number  of  persons  being  crowded  toge- 
ther in  a  place  illy  ventilated,  great  mortality 
ensued;  and  among  those  who  survived  the 
most  serious  form  of  disease  was  produced. 
The  instance  related  by  Dr.  Trotter,  of  the  fatal 
effects  arising  from  a  large  number  of  Africans 
being  closely  crowded  together  on  board  of 
the  slave  ships,  also  strongly  illustrates  this  fact, 
lie  savs,  "  I  have  often  observed  the  slaves  draw- 


(     14     ) 

ing  their  breath,  with  all  the  laborious  and  anxi- 
ous efforts  for  life  which  are  observed  in  expir- 
ing animals  subjected  to  foul  air,  or  under  the 
receiver  of  an  air-pump."  In  instances  similar  to 
these,  though  not  under  circumstances  so  afflict- 
ing, the  great  Lavoisier  instituted  experiments 
to  ascertain  the  changes  effected  upon  the  purity 
of  the  air.  This  was  done  at  the  principal  theatre 
in  the  city  of  Paris  during  the  play,  and  after 
the  conclusion,  in  which  the  house  was  much 
crowded.  He  here  found,  as  the  purity  of  the 
air  was  diminished,  the  effect  upon  the  audience 
was  very  perceptible  in  producing  great  languor 
and  inattention.  Similar  changes  resulted  from 
experiments  made  upon  the  air  of  the  closed 
wards  in  the  principal  hospital  of  France.  In 
order  to  understand  more  particularly  the  nature 
of  these  changes,  it  will  be  necessary  to  trace 
those  experiments  which  have  been  made  upon 
the  chemical  properties  of  our  atmosphere  as 
connected  with  animal  life. 

After  the  mechanical  effects  of  the  atmosphere 
had  been  investigated  by  philosophers,  chemists 
were  led  to  examine  more  particularly  into  its 
nature.  cc  It  had  been  considered  by  them  here- 
tofore as  an  homogeneous  fluid,  and  little  notice 
was  taken  of  it  in  their  operations;  for  when 
their  materials  vanished  in  air,  they  considered 
the  experiment  at  an  end,  and  stopped  at  that 
part  when  only  their  analysis  became  interest- 
ing. "*     Several  phenomena  had  been  observed* 

*  Bell's  Anatomy,  vol.  ii. 


(     15     ) 

which  led  to  a  more  particular  examination  of  its 
nature,  such  as  the  increased  weight  of  metallic 
bodies,  which,  when  burned  in  atmospheric  air, 
became  altered  in  their  properties  from  a  mild 
substance  to  a  caustic  drug; — the  support  given 
to  animal  life  and  flame  was  limited  according  to 
the  quantity  of  air  and  the  formation  of  acids  by 
combustion.  For  an  explanation  of  these  phe- 
nomena, we  are  greatly  indebted  to  the  investi- 
gations of  the  celebrated  Priestley.  He,  from  ex- 
tensive experiments  upon  aerial  fluids,  was  led 
to  a  particular  examination  of  the  atmosphere, 
and  proved  by  accurate  analysis,  that  it  was  made 
up  of  two  separate  airs,  to  which  he  gave  names 
expressive  of  their  different  natures.  The  larger 
and  impurer  part  he  called  phlogisticated  air;  the 
second  or  smaller  portion,  which  possessed  di- 
rectly opposite  effects,  he  denominated  dephlo- 
gisticated,  or  an  air  deprived  of  phlogiston. 

Scheele  was  led  to  the  same  conclusion  by 
a  different  course  of  experiments,  in  which  he 
was  engaged  at  nearly  the  same  time,  but  ap- 
plied different  names  to  the  result  of  his  inqui- 
ries. He  called  the  phlogisticated  air  of  Priest- 
ley foul  air;  to  the  dephlogisticated  he  gave  the 
name  of  empyreal  air,  or  an  air  pure  in  the  ex- 
treme. Lavoisier,  extensively  engaged  in  expe- 
riments upon  almost  all  substances,  and  without 
a  knowledge  of  what  had  been  done  by  the 
other  discoverers,  was  led  to  an  investigation  of 
the  same  subject,  and  drew  the  same  conclu- 
sions from  them,  but  applied  also  different  names, 
as  more  particularly  expressive  of  their  different 


(   16  ) 

effects  and  properties.  The  phlogisticated  air 
he  called  azotic  gas>  from  its  noxious  effects 
upon  animal  life  and  combustion ;  to  the  de- 
phlogisticated  he  gave  the  name  of  oxygen  gas* 
These  two  airs  he  found,  from  accurate  experi- 
ments, to  exist  in  the  proportion  of  seventy-three 
parts  of  azote  to  twenty-seven  of  oxygen  in  the 
hundred  of  all  uncontaminated  atmospheric  air. 
Later  chemists  have  added  another  gas  as  a  con- 
stituent part,  which,  however,  forms  only  a  small 
proportion;  but  its  strong  tendency  to  combine 
with  various  substances  whenever  it  is  generated 
in  any  considerable  quantity,  is  the  probable  cause 
of  its  not  being  reckoned  a  constituent  part  by 
some  chemists.  This  air  is  called  carbonic  acid 
gas,  from  its  having  carbon  as  its  base,  and 
from  the  uniform  disposition  which  that  sub- 
stance possesses  to  combine  with  oxygen.  It 
exists  in  the  state  of  an  acid,  possessing  greater 
specific  gravity  than  either  of  the  other  gasses, 
and  for  that  reason  is  supposed  to  be  found  only 
near  the  surface  of  the  earth. f 

Hydrogen  gas,  so  called  from  its  being  the 
base  of  water,  is  formed  from  numerous  sources, 
and  often  exists  in  the  air  we  breathe;  from  its 


*  Oxygen  gas  is  thus  denominated  from  its  base  being  necessary  in 
the  formation  of  all  acids. 

f  Sassnre  found  it  at  the  top  of  mount  Blanc,  the  highest  point  of 
the  old  continent ;  a  point  covered  with  eternal  snow,  and  not  exposed 
tc  the  influence  of  vegetables  or  animals.  Lime-water,  diluted  with  its 
own  weight  of  distilled  water,  formed  a  pellicle  on  its  surface  after  an 
hour  and  three  quarters  exposure  to  the  air  on  the  top  of  that  mountain ; 
and  slips  of  paper  acquired  the  property  cf  effervescing  with  acid  after 
being  exposed  for  half  an  hour  in  the  same  place.  Thompson's  Che- 
mistry, vol.  iii.  p.  284. 


(    n    ) 

possessing  less  specific  gravity  than  the  other  airs* 
it  occupies  the  higher  regions  of  the  atmosphere. 

Oxygen  exists  in  the  state  of  gas  by  being  com- 
bined with  caloric,  or  the  matter  of  heat  which 
is  separated  in  the  combustion  of  inflammable 
bodies,*  while  its  base  enters  into  combination 
with  the  combustible  substance  forming  (if  the 
union  be  complete)  an  acid,  as  with  sulphur; 
but  if  imperfect  or  partial,  a  calx  or  oxyd.  All 
bodies,  when  burned  in  this  gas,  are  rapidly  con- 
sumed, and  give  out  a  bright  flame  that  is  pain- 
ful to  the  sight.  Azotic  gas  is  also  united  with 
caloric;  it  is  lighter  than  common  air,  enters 
largely  into  animal  bodies  as  a  constituent  part, 
and  being  chemically  united  with  oxygen,  forms 
nitric  acid.  The  necessity  of  these  airs,  or  some 
one  of  them  in  particular,  in  respiration,  is  an 
obvious  fact,  and  is  best  ascertained  from  experi- 
ments made  upon  animals  when  breathed  in  an 
-uncombined  state. 

If  an  animal  be  confined  in  azotic  air,  its  life 
is  suddenly  destroyed,  and  the  effect  is  almost  as 
sudden  from  hydrogen  gas.  This,  however,  ap- 
pears to  be  contradicted  from  the  experiments  of 
Scheele  :  he  found  he  could  breathe  it  for  some 
time  without  much  difficulty.  The  same  ex- 
periment was  also  made  by  Pilatre  de  Rosier, 
and  nearly  with  fatal  consequences  upon  his  first 
respiring  it ;  but  afterwards  he  was  enabled  to 
continue  the  experiment  without  much  inconve- 

*  This  is  denied  by  Mr.  Davy  from  some  experiments  of  his.      See 
JScddoes'  Observations. 


(    is    ) 

nience  for  some  time.  This  experiment  was  re- 
peated by  Fontana:  he  ascertained  that  the  abi- 
lity to  breathe  this  gas  arose  from  the  common 
air  contained  in  his  lungs  when  he  began  to 
breathe.  Mr.  Davy  was  unable  to  breathe  hy- 
drogen, but  with  the  greatest  difficulty,  after  a 
complete  voluntary  exhaustion  of  his  lungs.  It 
produced  an  uneasy  feeling  in  his  chest,  momen- 
tary loss  of  muscular  power,  and  sometimes  a 
transient  giddiness.  The  probability  therefore  is, 
that  this  air  is  respirable  only  till  the  common 
air  contained  in  the  lungs  becomes  vitiated,  for 
they  always  contain  it  in  considerable  quantities. 
Forty  cubic  inches  of  air  is  the  quantity  usually 
taken  in  at  each  inspiration  ;  by  a  forced  expira- 
tion much  more  can  be  expelled:  hence  the 
lungs  are  supposed  to  contain,  at  their  utmost 
fulness,  not  less  than  two  hundred  and  twenty 
cubic  inches  of  air,  and  it  is  not  in  our  power 
to  empty  them  completely. 

The  fatality  of  carbonic  acid  gas  to  animal  life 
is  proved  from  numerous  instances;  as  that  of 
holding  animals  over  the  tubs  of  fermenting  beer, 
where  we  know  this  gas  is  generated,  or  over 
springs  from  which  it  is  thrown  off.  The  instances 
of  people  going  into  wine  cellars  that  have  been 
long  shut  up,  by  which  they  are  instantly  suf- 
focated, and  the  experiments  made  at  the  cele- 
brated Grotto  del  Cani  in  Italy,  to  satisfy  the  idle 
curiosity  of  travellers,  are  sufficient  evidences  of 
its  fatal  properties. 

These  gasses  then  being  evidently  proved  noxi- 
ous to  animal  life,  oxygen  is  that  part  alone  that 


(     19     ) 

remains  which  appears  essential  and  necessary; 
this,  in  an  increased  or  diminished  quantity,  ren- 
ders a  certain  portion  of  atmospheric  air  respira- 
ble  for  a  longer  or  shorter  time,  the  life  of  the 
animal  always  being  proportioned  to  the  quan- 
tity of  oxygen.  And  in  these  particulars  the 
same  facts  are  true  as  respects  combustion :  as  the 
quantity  of  oxygen,  in  a  limited  proportion  of 
air,  is  diminished,  the  flame  begins  to  decay,  and 
is,  at  length,  entirely  extinguished:  on  exami- 
nation this  air  is  found  to  be  entirely  consumed, 
while,  in  some  instances,  other  substances  are 
generated.  It  is  from  a  similarity  of  results  in 
the  experiments  upon  animal  life  and  combus- 
tion, that  this  process  has  been  concluded  to  be 
the  same,  which,  however,  is  contradicted  from 
some  known  facts  hereafter  to  be  enumerated. 

It  is  presumable,  from  the  facts  and  expe- 
riments that  have  been  detailed,  that  the  air 
answers  some  important  purpose  in  the  animal 
body;  and  from  its  coming  nearly  in  contact  with 
the  blood  while  it  circulates  through  the  lungs, 
separated  only  by  a  delicate  membrane,  it  may  be 
inferred,  that  this  becomes  the  medium  through 
which  the  necessary  changes  are  answered.  Some 
sensible  effect  may  therefore  be  rendered  evident 
upon  this  fluid,  as  so  frequent  a  change  becomes 
necessary  for  the  support  of  life.  These  effects 
may  be  judged  of  by  exposing  blood  to  the  in- 
fluence of  each  gas  out  of  the  body,  from  which 
we  may  probably  infer  the  importance  of  the 
oxygenous  portion. 

1st.  If  we  expose  a  quantity  of  venous  blood, 


(      20      ) 

which  is  of  a  dark  colour,  to  a  certain  quan- 
tity of  atmospheric  air,  it  becomes  of  a  bright 
colour,  and  the  air  is  diminished  in  quantity. 
This  change  of  colour  is  effected  not  only  by  an 
immediate  contact  of  air  with  the  blood,  but  the 
same  effect  is  produced  through  the  thick  coats 
of  a  bladder,  which  fact  was  first  noticed  by  Dr. 
Priestley. 

2d.  If  venous  blood  be  exposed  to  oxygen  gas 
alone,  the  change  in  colour  is  the  same,  but  the 
diminution  not  so  sensible;  and  in  this  experi- 
ment, agreeable  to  Girtanner,  a  quantity  of  hy- 
drogen and  carbon  are  given  out,  which  form 
water  and  carbonic  acid. 

3d.  Venous  blood  exposed  to  azotic  gas  un- 
dergoes no  change  in  its  colour,  neither  is  the 
gas  diminished  in  quantity;  but  if  arterial  blood 
be  exposed  to  its  influence,  it  becomes  of  the 
colour  of  venous  blood,  and  after  being  exposed 
for  a  short  time,  the  air  contained  in  the  bottle 
in  which  the  experiment  was  made,  was  found 
capable  of  supporting  animal  life  and  combustion  .* 

4th.  Venous  blood  exposed  to  carbonic  acid 
gas  becomes  of  a  brownish-red  colour,  and  the 
gas  is  slightly  diminished  in  quantity. 

5th.  Venous  blood  exposed  to  hydrogen  gas 
renders  the  colour  darker,  but  its  action  upon 
arterial  blood  is  to  render  it  suddenly  of  a  dark 
colour. 

These  experiments,  with  others  that  have  been 
made,  show  that  the  principal  apparent  change 

•  Venous  blood  possesses  the  power  of  decomposing  the  oxyd  of  azote, 
which  heightens  its  colour. 


(     21     ) 

wrought  upon  the  blood  is  in  the  colour;  and  that 
by  the  absorption  of  oxygen  it  is  also  capable  of 
giving  off  this  air  when  exposed  to  other  matters 
which  have  a  stronger  attraction  for  it,  as  is  also 
proved  by  the  experiments  mentioned  above. 

If  these  changes  are  effected  upon  blood  out 
of  the  body  by  the  influence  of  air,  it  becomes 
necessary  to  ascertain  whether  the  same  effect  is 
produced  upon  the  mass  of  venous  blood  while 
passing  through  the  lungs  of  animals  during  life  ; 
for  a  confirmation  of  which,  we  must  refer  to  the 
experiments  of  Hook,  Goodwyn,  and  Hunter. 
They  took  a  dog,  opened  the  chest,  removed  the 
pericardium,  and  kept  the  animal  alive  by  an  ar- 
tificial respiration.     Here  it  was  found  that  the 
blood  carried  to  the  lungs  by  the  pulmonary  artery 
was  of  a  dark  purple  hue,  answering  in  all  its 
appearances  to  that  of  venous  blood  in  other  parts 
of  the  body,  while  that  returned  to  the  heart  by 
the  pulmonary  veins  became  of  a  bright  Vermil- 
lion colour:  if  they  ceased  to  throw  in  air  this 
change  did  not  take  place ;  the  blood  returned  by 
the  veins  was  as  dark  as  that  brought  by  the 
artery;  a  diminution  of  the  pulsations  of  the  heart 
and  arteries  took  place,  and  finally  ceased.  These 
were  all  renewed  upon  air  being  again  thrown 
into  the  lungs;  and  life  was  in  this  way  suspended 
and  renewed  at  pleasure. 

From  the  similarity  of  change  effected  upon  the 
blood  both  in  and  out  of  the  body,  and  from  the 
immediate  connection  that  exists  between  it  and 
its  vital  actions,  we  may  justly  conclude  that  oxy- 
gen is  that  part  of  our  atmosphere  which,  when 


(    £2    ) 

combined  with  the  blood,  gives  the  vital  spring, 
as  it  is  immediately  applied  to  the  most  irritable 
muscular  organ  of  the  human  body,  and  which 
from  its  earliest  formation  is  highly  susceptible 
of  every  stimulating  impression,  and  capable  of 
maintaining  its  irritability  longer  than  any  other. 
This  principle  of  the  heart  is  more  accumulated 
upon  the  internal  surface  than  in  any  other  part.* 
If  the  air  of  expiration  be  examined,  it  will 
be  found  to  differ  materially  in  its  properties  from 
that  of  inspiration.  The  oxygen,  and  a  small  por- 
tion of  the  azote,  have  disappeared  ;  a  quantity  of 
carbonic  acid,  and  water  in  the  state  of  vapour, 
has  been  generated.  In  respect  to  the  quantity 
of  air  that  disappears  during  each  inspiration,  the 
experiments  of  different  chemists  vary :  Lavoisier 
and  Dr.  Menzies  made  it  one-twentieth  of  the 
air  inspired,  while  others  have  made  the  quan- 
tity greater  or  less,  according  to  the  perfection 
of  the  apparatus  with  which  the  experiments 
have  been  made,  and  the  accuracy  of  observation, 
These  chemists  confined  the  diminution  only  to 
the  oxygenous  portion  of  the  atmosphere,  while 
the  later  experiments  of  Mr.  Davy  have  confirmed 
the  supposition  of  Dr.  Priestley,  that  a  certain 
portion  of  azote  as  well  as  oxygen  was  absorbed 
by  the  venous  blood.  He  found  by  repeated  ex- 
periments, the  average  quantity  of  air  that  disap- 
pears to  be  1.4  of  a  cubic  inch,  of  which  0.2  are 


*  It  is  a  position  that  has  been  considerably  contended  for,  whether 
the  heart  derived  its  principle  of  irritability  from  the  oxygen  of  the  air ; 
whether  it  was  a  principle  derived  from  another  source,  or  resident  within 
itself.  The  former  position  has  been  strongly  contended  for  by  Girtan* 
p.ex  and  other  pneumatic  physiologists. 


(     23     ) 

azote  and  1.2  oxygen.  This,  allowing  twenty-six 
respirations  per  minute,  which  is  about  the  ave- 
rage number,  amounts,  in  twenty-four  hours,  to 
rather  more  than  thirty-eight  ounces  of  air,  or 
precisely  4.68  of  azote,  and  33.54  of  oxygen* 

That  carbonic  acid  gas  exists  in  the  air  of  ex- 
piration, is  proved  from  the  simple  experiment 
of  breathing  through  lime-water,  which  renders 
it  turbid  by  the  new  combination  that  is  formed: 
the  carbonic  acid  unites  with  the  lime  that  is  sus- 
pended in  the  water,  and  forms  a  carbonate  of 
lime  that  is  insoluble. 

That  water  is  also  continually  passing  off  from 
the  lungs  in  the  state  of  vapour,  is  rendered  evi- 
dent to  every  one  that  breathes  in  a  cold  atmos- 
phere, or  upon  the  surface  of  a  polished  body, 
by  the  condensation  that  takes  place.  Whe- 
ther these  substances  are  formed  in  the  lungs  by 
the  combination  of  the  oxygen  with  the  hydro- 
carbon that  is  thrown  off  from  the  blood,  or, 
whether  they  are  formed  during  its  circulation 
through  the  body,  remains  a  question  not  satis- 
factorily determined  from  experiments.  As  far 
however  as  experiments  have  been  directed  to 
the  particular  investigation  of  this  subject,  their 
results  favour  the  latter  opinion.  From  a  collec- 
tion of  these  facts,  it  follows  to  investigate  how 
far  they  may  tend  toward  an  explanation  of  the 
phenomena  of  animal  heat. 

It  is  a  singular  property  which  animals  possess 
of  supporting  a  standard  degree  of  temperature 

*  Thompson's  Chemistry. 


{     24     ) 

in  every  vicissitude  of  climate.*     Thus  we  find 
that  the  degree  of  temperature  is  the  same  in  the 
coldest  regions  of  the  earth  where  man  can  exist, 
and  where  even  mercury  may  become  solid,  as 
well  as  in  the  higher  ranges  of  temperature  up  to 
that  of  boiling  water,  as  was  proved  from  the 
experiment  of  Dr.  Fordyce  and  others.     In  this 
extreme  degree  of  heat,  they  found  the  body  sup- 
ported its  standard  degree  of  temperature,  that  of 
98  deg.  And  it  is  even  said,  that  man,  by  habit, 
may  become  able  to  bear  a  much  greater  extreme. 
In  the  different  classes  of  animals,  there  is  a 
considerable  variety  in  the  heat  of  their  bodies. 
This  variety  is  dependant  upon  the  perfection  of 
their  respiratory   organs,  and  their  capability  to 
take  in  a  large  proportion  of  air.     As  for  exam- 
ple, in  birds,  where,  from  the  particular  struc- 
ture of  their  lungs,  the  blood   is  exposed  to  the 
extensive  influence  of  air,  their  temperature  ex- 
ceeds an  hundred  degrees  of  Fahrenheit's  ther- 
mometer. 

In  the  lower  classes  of  animals,  or  what  are 
called  the  cold-blooded,  their  heat  exceeds  very 
little  the  medium  in  which  they  live.  In  these 
animals,  the  process  of  respiration  is  slow,  and 
the  quantity  of  air  that  is  absorbed  is  small. 
They  retain  their  irritability  longer  than  the  more 
perfect  animals,  and  suffer  less  from  any  injury 
which  they  receive.  Their  power  of  generating 
heat  is  not  sufficient  to  prevent  them   from  be- 


*   This  power,  from  experiments,  appears  to  extend  also  to  vegetables 
a  very  considerable  decree.    Their  standard  temperature  does  not 
:ceed  56  deg. 


{     25     ) 

coming  torpid  during  the  severities  of"  winter,  but 
are  soon  renovated  from  the  warmth  of  spring. 

The  standard  heat  of  animal  bodies  is  regu- 
lated not  only  by  the  nature  of  the  air  taken  in, 
but  by  a  function  of  its  own,  the  cutaneous  per- 
spiration:  for,  in  the  extremes  of  cold,  we  not 
only  take  in  a  larger  proportion  of  vital  air,  by  a 
condensation  from  a  diminished  temperature, 
fbut  the  perspiration  is  in  less  quantity,  and  a 
portion  of  heat  is  retained.  When  respiration 
becomes  quickened  from  any  cause,  the  heat  of 
the  body  is  increased,  and  continues  so  until  a 
proportional  increase  of  perspiration  subducts 
the  superabundant  heat  from  the  system.  As  it 
is  an  established  law,  that  in  proportion  as  aque- 
ous fluids  are  converted  into  insensible  vapour, 
caloric,  or  the  matter  of  heat  is  absorbed. 
These  facts  are  particularly  exemplified  in  walk- 
ing more  rapidly  than  usual,  or  in  any  other 
species  of  exercise  which  calls  a  number  of 
muscles  into  considerable  and  continual  action; 
and  in  fever,  where  the  perspiration  becomes  ob- 
structed; while  the  actions  of  the  heart  and  ves- 
sels are  increased,  and  the  respiration  propor- 
tionably  quickened,  the  heat  will  be  more  con- 
tinued, and  is  diminished  only  by  a  free  dis- 
charge of  perspirable  matter.  In  high  degrees  of 
temperature,  the  air  we  breathe  is  much  rari- 
fied,  and  a  much  less  quantity  of  vital  gas  res- 
pired in  an  equal  volume  of  air;  while,  at  the 
same  time,  the  cutaneous  perspiration  is  much 
more  increased,  and  its  vicarious  discharge,  that 
by  the  kidneys,  diminished.     We  are  hence  en- 


(     26     ) 

abled  to  live  under  every  vicissitude  of  climate 
and  season.  The  different  opinions  which  have 
been  offered  to  explain  this  property  of  animal 
bodies,  admit  of  considerable  diversity,  even  af- 
ter the  importance  and  influence  of  air  was  un- 
derstood from  experiments.  Dr.  Priestley  made 
respiration  to  consist  in  an  elimination  of  a  noxi- 
ous principle  from  the  blood,  which  is  thrown 
off  from  that  brought  to  the  lungs  by  the  pul- 
monary artery,  for  which  the  air  of  inspiration 
has  a  stronger  affinity  than  the  blood,  and  when 
separated  renders  it  of  a  bright  colour.  This  prin- 
ciple is  denominated  phlogiston.  It  was  this 
theory  that  was  adopted  and  improved  upon  by 
Crawford  and  Elliot,  by  means  of  which  they  at- 
tempted the  explanation  of  the  different  pheno- 
mena of  animal  heat ;  saying  that  in  proportion 
as  the  blood  parted  with  phlogiston  its  capacity 
for  containing  fire  became  increased,  which  it 
absorbed  from  the  air,  and  distributed  to  every 
part  of  the  body.  The  exceptions  to  this  doc- 
trine are  obvious ;  for  the  explanation  is  entirely 
dependant  upon  an  assumed  principle,  of  whose 
evidence  we  have  no  certainty,  and,  of  course, 
are  incapable  to  judge  of  its  properties.  The 
theory  of  Lavoisier  is  similar  to  that  of  Priestley, 
differing  only  in  terms.  His  opinion  was,  that 
the  quantity  of  oxygen  was  diminished  by  its 
combining  with  hydrogen  and  carbon,  to  form 
water  and  carbonic  acid  gas;  at  the  same  time  a 
portion  of  caloric  was  given  to  the  blood.  This 
theory  is  incorrect,  inasmuch  as  it  asserts  the 
combination  of  hydrogen  and  carbon  at  a  lower 


(     27     ) 

temperature  than  is  evident  from  experiments 
out  of  the  body,  where  the  decomposition  does 
not  take  place  in  any  instance  without  the 
production  of  flame.  Lavoisier,  however,  did 
not  prove  this  theory  from  experiments;  it  was 
the  subject  in  which  he  was  engaged  when 
cut  off  by  the  tyrannical  hand  of  Robespierre, 
The  theory  of  Le  Grange  differs  somewhat 
from  that  of  Lavoisier.  He  has  asserted  that  a 
portion  of  oxygen  is  taken  up  by  the  blood  in  the 
lungs,  and  at  the  same  instant  a  quantity  of  wa- 
ter and  carbonic  acid  are  given  out.  This,  how- 
ever, makes  the  lungs  still  the  fire-place  of  the 
system,  and  besides  allows  only  the  oxygenous 
portion  of  the  atmosphere  to  be  absorbed,  which 
is  contradicted  by  the  experiments  of  Mr.  Davy, 
as  mentioned  above,  whose  theory  appears  liable 
to  the  least  objections.  He  considers  the  blood, 
while  passing  through  the  lungs,  to  absorb  air  in 
an  undecomposed  state,  which  it  carries  through 
the  bloodvessels.  In  the  course  of  the  circulation 
this  air  is  gradually  decomposed,  the  oxygen 
of  the  azote  entering  into  new  combinations, 
while  a  portion  of  azote  and  carbonic  acid  are 
evolved.  On  returning  to  the  lungs,  the  blood 
receives  a  fresh  supply  of  air,  and,  at  the  same 
time,  discharges  the  azotic  gas,  carbonic  acid 
gas,  and  watery  vapour  formed  during  the  cir- 
culation. 

From  the  experiments  of  Mr.  Davy,  respecting 
a  diminution  of  a  portion  of  the  azotic  part  of 
the  atmosphere,  some  new  reasoning  upon  the 
process  of  respiration  may  be  introduced:  for,  be- 


(     28     ) 

fore  these  experiments,  the  writers  upon  this  sul> 
ject  confined  themselves  to  an  investigation  of 
those  substances  in  the  blood  that  should  account 
for   the  strong  affinity  that  existed  between  it 
and  oxygen.     Accordingly  iron,  whose  presence 
is  universally  proved  to  exist  in  all  animals  that 
possess  red  blood,  was  considered,  from  its  rea- 
diness to  combine  with   oxygen,    as  best  calcu- 
lated to  explain  the  change  produced.     cc  But 
as  the  temperature  at  which  this  oxydation  takes 
place  is  not  sufficiently  great  to  account  for  that 
instantaneous   change   which  the  blood  under- 
goes in  the  lungs,  or  when  exposed  to  the  influ- 
ence of  oxygen  out  of  the  body,  it  is  therefore 
necessary  to  call  in  some  other  of  the  component 
part  of  the  blood  ;  and  as  phosphorus  is  always 
found  in  the  blood  of  animals,  and  its  attraction 
for  oxygen  is  very  strong,  and  that  at  a  low  tem- 
perature, it  explains  more  satisfactorily  the  ef- 
fect produced."*     If  these  then  are  the  substan- 
ces with  which  the  oxygen  combines,  to  what  is 
the  azote  united  ?  We  are  told  by  Mr.  Davy,  that 
the  blood  becomes  completely  animalized  in  the 
lungs.     If  this  be  the  fact,  it  may  be  explained 
why  so  small  a  portion  of  the  azote  disappears,  for 
the  discharge  of  chyle  into  the  subclavian  vein  is 
slow  and  gradual,  and  this  absorption  must  be  in 
that  proportion ;  and  as  azote  is   a   constituent 
part  in  all  animal  bodies,  whether  their  food  be 
taken  from  the  animal  or  vegetable  kingdom, 
its  appearance  upon  their  decomposition,  in  conn 

*  Youle  on  Respiration. 


(     29     ) 

giderable  quantities,  and  its  production  as  the 
result  of  chemical  experiments,  are  facts  that 
lead  us  to  conclude,  that  azote  enters  into  com- 
bination with  the  animal  fibre,  as  derived  from 
the  air  through  the  lungs,*  These  discoveries 
show  that  what  is  fatal  to  animal  life  in  an  un- 
combined  state,  is  necessary  to  it  when  combined, 
and  demonstrates  the  economy  of  nature  in  the 
regular  preservation  and  support  of  life. 

Oxygen  gas,  when  breathed  in  a  pure  state, 
gives  new  vigour  to  animal  life,  quickens  the  cir- 
culation, increases  the  heat  of  the  system,  pro- 
motes digestion,  and  is  said  to  produce  the  most 
pleasurable  sensations.  The  sense  of  heat  in  these 
instances  has  been  said  to  begin  in  the  lungs  as  a 
centre,  and  to  be  diffused  from  thence  more  gene- 
rally over  the  body.  These  experiments  were 
however  closely  connected  with  the  establishment 
of  a  favourite  hypothesis,  and  the  sensations  were 
felt  more  evidently  by  the  authors  than  by  disinter- 
ested persons.  That  oxygen  is  however  a  power- 
ful stimulus  is  an  acknowledged  fact,  and  like  all 
other  powerful  stimuli,  when  continued  for  some 
time,  destroys  the  animal  machine.  Azote  may 
therefore  answer  a  further  purpose  in  the  animal 
economy,  that  of  properly  tempering  the  air,  be- 


*From  some  late  experiments  that  have  been  made  by  Dr.  J.  Ley- 
merie,  of  France,  he  has  found  that  ammonia  is  one  of  the  essential 
parts  in  the  formation  of  red  blood.  Now,  as  the  component  parts  of 
this  substance  are  azote  and  hydrogen,  we  are  again  shown  the  neces- 
sity of  a  supply  of  the  former  material  in  order  to  answer  the  essential 
properties  of  an  animal  fluid.  He  has  succeeded  in  converting  milk  into 
blood  by  the  addition  of  pure  ammonia  in  certain  adjusted  proportions, 
within  a  given  time.  A  more  full  account  of  his  experiments  will  pro- 
bably soon  be  given  to  the  public. 


(    so    ) 

sides  allowing  of  a  more  extensive  exposure  of 
blood  in  the  lungs,  to  the  influence  of  that  quan- 
tity of  oxygen  that  is  necessary  to  the  support  of 
life,  by  inflating  them  with  a  gas  whose  stimulant 
properties  are  not  so  powerful,  but  whose  presence 
is  at  the  same  time  equally  necessary.  This  po- 
sition, therefore,  appears  consistent,  inasmuch  as  it 
explains  many  of  the  phenomena  connected  with 
animal  life. 

The  following  conclusions  may  then  be  drawn 
from  the  facts  and  experiments  detailed :  1  st.  That 
respiration  is  of  use,  by  imparting  oxygen  to  the 
system  through  the  medium  of  the  blood  circu- 
lated in  the  lungs,  for  the  principal  purpose  of 
giving  heat  to  the  body  by  the  new  combinations 
that  are  formed.  Of  this  we  are  convinced  di- 
rectly from  experiments.  Mr.  Davy  took  blood 
from  the  carotid  artery  of  a  calf,  enclosed  it  in  a 
phial,  to  which  was  affixed  a  pneumatic  appara- 
tus; it  was  then  exposed  in  a  sand  bath  to  a  tem- 
perature of  96  deg.  gradually  increased  to  108  deg. 
The  blood  now  began  to  coagulate,  some  glo- 
bules of  gas  were  emitted;  the  temperature  of 
the  bath  was  raised,  and  the  blood  became  of  a 
dark  colour.  On  examining  the  nature  of  the 
air  disengaged,  it  was  found  to  be  oxygen,  with 
a  small  quantity  of  carbonic  acid.*  We  are  also 
convinced  that  oxygen  is  absorbed  by  the  blood 
from  its  presence  p  many  of  the  secretions  and 
excretions  formed  from  this  fluid;  as  in  the  urine, 
where  it  is  discovered  passing  ofT  as  excrementi- 

*  Beddoes'  Observations. 


(     31     ) 

tious  in  the  form  of  an  acid.  In  the  bones  it  has 
entered  into  union  with  calcareous  matter  when 
combined  with  phosphorus.  In  the  fat  of  ani- 
mals a  particular  acid  is  also  discoverable.  The 
formation  of  acids  in  these  different  secretions 
depend  upon  the  presence  of  oxygen,  as  it  is  an 
acknowledged  principle  in  chemistry,  without  it 
no  acid  can  be  formed.  If  oxygen  then  be  main- 
tained in  its  gaseous  state  by  means  of  caloric, 
its  decomposition  and  new  union  must  have  set 
it  free.  It  is  therefore  probable  that  oxygen  is 
decomposed  in  the  extreme  vessels ;  for,  as  far  as 
we  have  yet  become  acquainted  with  secretion 
from  the  ultimate  structure  of  glands,  the  pro- 
cess appears  to  be  effected  in  the  extreme  arteries. 
And  further,  while  a  partial  action  of  the  minute 
ramifications  of  arteries  become  excited,  as  in 
local  inflammation,  a  preternatural  heat  is  accu- 
mulated without  an  increase  of  respiration:  but 
this  effect  cannot  be  produced  to  any  considera- 
ble extent  without  an  increase  of  arterial  action, 
which  produces  a  disease  of  the  whole  body.  This 
fact  is  more  particularly  exemplified  where  the 
principal  arterial  trunk  of  a  limb  is  tied  up,  and  the 
circulation  is  to  be  carried  on  by  the  small  anas- 
tamosing  branches.  Here  at  first  the  limb  is  cold, 
until  the  blood  begins  to  find  its  way  by  the  mi- 
nute vessels  which  are  excited  into  great  action, 
the  heat  becomes  preternaturally  accumulated, 
and  continues  so  until  some  of  the  branches  are 
sufficiently  dilated  to  transmit  the  former  quan- 
tity of  blood. 

2d+  The  union  which  has  taken  place  between 


(     32     ) 

the  chyle  and  azote,  as  a  constituent  part,  and 
which  has  now  become  of  the  nature  of  blood* 
in  all  respects  fit  to  answer  its  purposes  in  the 
body,  of  forming  new  secretions,  generating  new 
parts,  and  effecting  every  property  which  is  ne- 
cessary in  the  maintenance  of  the  animal  body. 

It  is  a  fact  admitted  by  physiologists,  in  which 
they  have  been  aided  by  the  experiments  of  the 
chemist,  that  the  coagulable  lymph  is  that  por- 
tion of  the  blood  approaching  the  nearest  to  the 
nature  of  the  animal  fibre;  and  from  this  property 
the  inference  is  consistent,  that  it  is  more  parti- 
cularly calculated  to  answer  every  purpose  of  nu- 
trition to  the  body,  the  wastes  of  the  machine 
are  continually  going  on,  and  it  is  necessary 
that  they  should  be  as  continually  repaired.  From 
these  different  changes,  is  it  not  probable  that 
the  animal  heat  is  in  some  degree  assisted  in 
its  regular  maintenance  ?  It  must  also  be  admit- 
ted, that  as  azotic  gas  enters  into  union  with 
the  coagulable  lymph  to  render  it  of  the  nature 
of  the  animal  fibre,  it  also  parts  with  its  caloric 
in  the  same  manner  as  the  oxygen.  And  it  is 
an  established  law,  that  as  gaseous  substances 
assume  the  solid  form,  their  caloric  is  set  free; 
this  heat  being  disengaged  from  its  base,  which 
has  formed  a  union,  assists  itself  also  in  answer- 
ing a  useful  purpose. 

Animal  heat  may  therefore  not  be  dependant 
upon  the  respiration  of  oxygen  alone,  but  upon  the 
absorption  of  azote  also,  which  two  gasses  are  so 
changed  by  means  of  vascular  action,  that  their 
bases  enter  into  union  with  the  body  to  answer 


(     S3     ) 

useful  purposes  in  the  animal  economy.  And  it 
is  by  means  of  these  changes  that  the  regular  main- 
tenance of  animal  heat  is  kept  up,  subject  to 
irregularities  from  increased  respiration  and  di- 
minished perspiration,  as  in  fevers  and  active  exer- 
cise ;  regulated  also  in  colder  climates  by  the 
volume  of  air  being  more  condensed  and  perspi- 
ration lessened.  These  facts  may  be  consider- 
ed fully  evident,  yet  the  chemical  changes  that 
occur  in  the  animal  body  are  so  obscure,  that  it 
will  require  a  number  of  well  conducted  expe- 
riments before  every  objection  can  be  answered 
that  may  be  urged  against  the  opinions  advanced, 
which  the  genius  for  improvement  appears  to  be 
rapidly  investigating. 


THE  END 


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